Yarn having differentiated shrinkage segments and fabrics formed therefrom

ABSTRACT

A multi-filament yarn including interlace nodes disposed along the length of the yarn. The yarn has variable retained heat shrinkage potential at segments along its length such that segments of said yarn containing the interlace nodes have a retained heat shrinkage potential in excess of segments of said yarn between the interlace nodes. Upon application of uniform heat to the yarn, the segments containing the interlace nodes exhibit enhanced shrinkage and self texturing relative to the segments between the interlace nodes. A fabric formed with the yarn prior to the final heating process will present a varied and random appearance after application of the final heating process due to the differentiated shrink segments. Pile fabrics formed with the yarn as the pile yarn prior to the final heat treatment will have piles of varying height due to the differentiated shrink segments, and will also have a varied or random appearance.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of prior co-pending U.S. application Ser. No. 10/613,240, filed Jul. 3, 2003, entitled “Pile Fabric and Heat Modified Fiber and Related Manufacturing Process”, and a continuation-in-part of prior co-pending U.S. application Ser. No. 10/613,241, filed Jul. 3, 2003, entitled “Method of Making Pile Fabric”, and a continuation-in-part of prior co-pending U.S. application Ser. No. 10/835,772, filed Apr. 30, 2004, entitled “Loop Pile Fabric Having Randomly Arranged Loops of Variable Height”, and a continuation-in-part of prior co-pending U.S. application Ser. No. 10/835,763, filed Apr. 30, 2004, entitled “Textile Fabric Having Randomly Arranged Yarn Segments of Variable Texture and Crystallinity”, and a continuation-in-part of prior co-pending U.S. application Ser. No. 10/835,773, filed Apr. 30, 2004, entitled “Yarn Having Variable Shrinkage Zones”, the contents of all of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates generally to fabric formation yarns and more particularly to multifilament yarns in which discrete segments along the length undergo enhanced selective shrinkage resulting in self texturing and reduced crystalline orientation relative to other portions of the same yarn. The present invention also relates to various fabrics formed with the multifilament yarns having discrete segments of differing shrinkage.

BACKGROUND OF THE INVENTION

In the past, partially oriented yarns (POY) of multi-filament construction have typically been drawn and heatset under tension so as to extend and orient the individual filaments. In such a process each of filaments in the yarn is subjected to a substantially uniform heating and extension treatment such that the yarn will thereafter act in a uniform manner upon post fabric formation treatments such as heat setting, dyeing and the like. That is, since the yarn has been uniformly treated it does not exhibit variable response characteristics in a fabric when subjected to heating or other treatment conditions.

It is also known to under draw yarns under uniform heat treatment to less than full orientation for subsequent formation into a fabric. Such a process is illustrated and described in U.S. Pat. No. 5,983,470 to Goineau the contents of which are incorporated herein by reference in their entirety. The resultant fabric has a generally striated appearance upon dyeing.

SUMMARY OF THE INVENTION

According to one aspect, the present invention provides advantages and alternatives over the known art by providing a fabric formation yarn having variable shrink characteristics at different segments (also referred to as zones) along its length such that when such yarn is subsequently subjected to heat such as in fabric finishing treatments, discrete portions of the yarn undergo selective shrinkage and self texturing. The shrinking of segments along the yarn yields unshrunken yarn segments of substantially parallel, oriented fibers in combination with shrunken yarn segments of self textured filaments with reduced crystalline orientation in the same yarn.

According to another aspect, the present invention incorporates the yarn having differentiated segment shrink characteristics into a knit fabric so that when the fabric is subjected to a heat treatment, such as heated finishing and/or dyeing at elevated temperature, discrete portions of the yarn shrink preferentially thereby tightening up sections of the looped underlaps. This tightening causes the portions of the yarn which do not shrink to become raised in the fabric face. The shrinking of segments along the surface-forming yarn yields substantially random arrangements of unshrunken yarn segments of substantially parallel fibers in combination with shrunken yarn segments of self textured filaments with reduced crystalline orientation in the same yarn. The resultant fabric has an irregular surface appearance and surface texture.

According to yet other aspects, the present invention utilizes the yarn having differentiated segment shrink characteristics as the loop pile yarns in a loop pile fabric and the cut pile yarns in a cut pile fabric. The pile yarn has variable shrink characteristics at different zones along its length such that when the pile-forming yarn is introduced into a loop pile fabric and is thereafter subjected to heated finishing treatments, discrete portions of the yarn shrink towards the base of the fabric. The shrinking of zones along the pile-forming yarn towards the fabric base yields substantially random arrangements of unshrunken high pile zones in combination with shrunken lower pile zones of self textured crimped filaments with reduced crystalline orientation in the same yarn. The resultant fabric has an irregular pebble appearance.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described by way of example only, with reference to the accompanying drawings which constitute a portion of the specification herein and wherein:

FIG. 1 illustrates schematically a practice for hot drawing a multi-filament yarn to impart variable shrink characteristics at zones along the length of such yarn;

FIG. 2 illustrates a partially oriented non-textured multi-filament yarn prior to hot drawing;

FIG. 3 is a graphical representation illustrating the cross-sectional profile of yarn filaments at different zones along the length of the yarn of FIG. 3 during hot drawing;

FIG. 4A is a photomicrograph of fiber cross-sections in low shrink portions of a formation yarn according to the present invention;

FIG. 4B is a photomicrograph of fiber cross-sections in high shrink portions of a formation yarn according to the present invention at the same magnification as FIG. 9;

FIG. 5 is a photomicrograph of a circular knit sock illustrating variable shrinkage segments of a fabric formation yarn;

FIGS. 6A and 6B are x-ray diffraction patterns for high shrink and low shrink portions of a formation yarn respectively;

FIGS. 7A and 7B are angular distribution plots of select diffraction peaks for high shrink and low shrink portions of a formation yarn respectively;

FIG. 8 is a block diagram setting forth steps for forming a variable surface texture fabric;

FIG. 9 illustrates a surface view of a representative prior art flat knit fabric of uniform surface character;

FIG. 10 illustrates a knit fabric of construction similar to FIG. 9, incorporating the surface forming yarn with variable shrinkage zones following hot drawing and post formation heat treatment wherein zones of the surface forming yarn have undergone selective shrinkage and self texturing;

FIG. 11 illustrates a cut-away cross-section of a typical prior art loop pile fabric;

FIG. 12 illustrates a loop pile fabric incorporating the pile-forming yarn following hot drawing and post formation heat treatment wherein zones of the pile-forming yarn have undergone shrinkage towards the base of the fabric;

FIG. 13 is a photomicrograph of an exemplary loop-pile fabric according to the present invention incorporating high loops of unshrunken character and lower loops which have undergone heat shrinking;

FIG. 14 illustrates a cut-away cross-section of a typical prior art cut pile fabric;

FIG. 15 illustrates a cut pile fabric incorporating the pile-forming yarn following hot drawing and post formation heat treatment wherein zones of the pile-forming yarn have undergone shrinkage towards the base of the fabric; and,

FIG. 16 is a photomicrograph of an exemplary cut-pile fabric according to the present invention incorporating high loops of unshrunken character and lower pile yarns which have undergone heat shrinking.

While the present invention has been generally described above and will hereinafter be described in greater detail in relation to certain illustrated and potentially preferred embodiments, procedures and practices it is to be understood that in no event is the invention to be limited to such illustrated and described embodiments, procedures and practices. Rather, it is intended that the invention shall extend to all embodiments, practices and procedures as may be embodied within the broad principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Yarns With Segmented Differential Shrinkage Potential

Referring to FIG. 1, according to a potentially preferred practice of the present invention a yarn sheet 30 formed from a plurality of yarns 100 is passed from a creel 31 through a drawing apparatus 32 to a take-up 33. The yarns 100 are so called “partially oriented yarns” of multi-filament construction wherein the filaments 101 (FIG. 2) have been interlaced at discrete zones along the length of the yarn. In practice it is contemplated that the yarns are formed from a heat shrinkable material, such as a thermoplastic. By way of example only and not limitation, exemplary fiber materials may include polyester, polypropylene, nylon and combinations thereof. As will be appreciated, when such materials are extruded from a melt solution into drawn filaments, those filaments have an intrinsic finite shrinkage potential which is activated upon subsequent heat exposure. During heat exposure shrinkage will proceed until the shrinkage potential is exhausted or the heating is terminated.

As shown, the drawing apparatus 32 has a first draw zone 36 located between tensioning rolls 38, 40 and a second draw zone 42 located between tensioning rolls 40 and 46. A contact heating plate 50 as will be well known to those of skill in the art engages the yarns 100 within the second draw zone 42. According to the potentially preferred practice, the partially oriented yarns 100 are passed through the first draw zone 36 with substantially no heating or drawing treatment. Thus, the yarns 100 are substantially unaltered upon entering the second draw zone 42. At the second draw zone the yarns 100 preferably undergo a relatively slight drawing elongation while simultaneously being subjected to a relatively low temperature heating procedure from the contact heater 50. Since the resultant yarn 100′ is not drawn to a condition of full orientation it is referred to as “underdrawn” yarn. By “underdrawn”, it is meant that the fiber is still partially oriented and has a residual elongation of at least about 40%.

However, the resultant yarn 100′ of the present invention differs from a typical “underdrawn” yarn. According to the potentially preferred practice the yarn 100 is conveyed across the contact heater 50 at a high rate of speed such that the yarn does not reach a state of temperature equilibrium within the cross-section of the yarn at all segments along its length. As a consequence, the resultant yarn 100′ has discrete segments along its length that have been heatset to a greater extent than other segments. The segments of the resultant yarn 100′ that have a different extent of heat history will also have a different potential of shrinkage when heat is applied to the resultant yarn 100′.

By way of example only, and not limitation, for a 115 denier polyester yarn it has been found that subjecting such yarn to a draw ratio of about 1.15 (i.e. 15% elongation) with a contact heater temperature of about 170 C to about 200 C with a take up speed of about 600 yards per minute provides the desired non-uniform cross-sectional heat treatment at some segments of the yarn while yielding a uniform cross-sectional heat treatment at other segments. Of course, the level of drawing, temperature and speed may be adjusted for different yarns.

The mechanism believed to be responsible for the non-uniform character of the resultant yarns 100′ is believed to relate to the nature of the partially oriented yarn 100 being processed as well as the process conditions. Referring to FIG. 2, a representative illustration is provided of a partially oriented yarn (POY) 100 such as may be treated according to the practice described above. As illustrated, the yarn 100 of partially oriented construction is characterized by loose segments 102 in which the individual filaments 101 are disposed in generally parallel aligned loose orientation relative to one another. These loose segments 102 are interspersed by discrete interlace nodes 103 in which the filaments are interlaced in a more compacted relation so as to hold the overall yarn 100 together. The cross-sectional heat transfer characteristics of the loose segments 102 are believed to be substantially different from that of the interlace nodes 103 and the yarn portions immediately adjacent such nodes.

In FIG. 3 a graphical illustration of the fiber cross-section is provided showing the relative response of the filaments 100 in the loose segments 102 and interlace nodes 103 of the yarn during heating under slight draw conditions as described above. In particular, what is seen is that the filaments within the loose segments 103 are spread out closer to the heater by a combination of tensioning and heat shrinkage so as to assume a relatively low cross-sectional profile orientation across the contact heater 50. This low cross-sectional profile allows those zones to receive a substantially uniform and complete heat treatment despite the high speed of travel across the heater. Conversely, the relatively slight degree of draw applied is inadequate to pull out the interlace nodes 103. Thus, flattening and spreading of the filaments at the interlace nodes is avoided. Thus, upon high speed underdrawing conditions the yarn portions around the interlace nodes 103 retain a higher more concentrated profile across the heater 103 rather than flattening out like the loose segments 102.

It is surmised that due to the lack of flattening and the high rate of travel across the heater, heat treatment is not uniform within the interlace nodes and adjacent portions. Thus, a significant number of the filaments at those areas retain a relatively high level of shrinkage potential since a steady state temperature is not reached. The retention of such shrinkage potential leaves such segments susceptible to subsequent enhanced heat shrinkage relative to the remaining portions of the yarn (which have been subjected to uniform temperature treatment) upon subsequent heat application.

By way of example only, within a yarn 100′ according to the present invention it is contemplated that the number of interlace nodes will preferably be in the range of about 8 to 40 nodes per meter with each node taking up about 0.6 to about 1.3 cm. Thus, it is contemplated that zones of high retained shrinkage potential will preferably make up about 4.8% to about 52% percent of the total length of the yarn and will more preferably make up about 25% of the total length of the yarn.

The resultant yarn 100′ may then be formed into a fabric and heat treated to provide desired surface characteristics in the manner as will be described further hereinafter. Of course, it is also contemplated that the resultant yarn 100′ may be subjected to heat treatment prior to introduction into a fabric if desired. In either case, particular discrete segments of the yarn 100′ undergo shrinkage and self-texturing during subsequent heating of the resultant yarn 100″ while other segments along the same yarn experience little if any change.

Variable Shrinkage and Bulking

The enhanced retained shrinkage potential of the resultant yarn 100′ at the interlace nodes relative to the intermediate loose zones following the treatment process as outlined above has been confirmed by cutting out segments of an exemplary 260 denier polyester yarn treated according to the procedure outlined above and thereafter subjecting those cut out segments to a uniform heat treatment and then measuring the level of shrinkage caused by the heat treatment. In particular, a first group of two yarn segments was cut out from sections between interlace nodes such that each of the two cut out yarn segments in this first group was substantially devoid of any interlace node. A second group of three yarn segments was cut out from the yarn such that each of the three cut out yarn segments in this second group was formed substantially of a single interlace node. Both the first group and the second group of yarn segments were then subjected to a high temperature superheated steam treatment to observe shrinkage. The results are set forth in Table I below showing that the second group of yarn segments formed from the interlace nodes exhibited substantially increased shrinkage on a percentage basis relative to the yarn segments in the first group devoid of interlace nodes. TABLE I Percent Shrinkage Sample Segment After Heat Treating Sample 1 - Interlace Node Segment 43% Sample 1 - Interlace Node Segment 40% Sample 1 - Interlace Node Segment 33% Sample 4 - No Interlace Nodes 10% Sample 5 - No Interlace Nodes  0%

In addition to shrinkage, it was also observed that the yarn segments formed from the interlace nodes of the resultant yarn 100′ underwent an enhanced degree of bulking and self texturing when subjected to post treatment heating, resulting in substantial filament thickening in a significant portion of the filaments. In this regard it is to be understood that the terms “self texturing” or “self-crimping” refers to the characteristic that the filaments have a crimped construction after shrinkage without the application of external crimping or texturizing procedures. It was also discovered that the shrinkage and self texturing of those sections of yarn caused the cross section in those sections of the yarn to enlarge.

By way of example only, for purposes of comparison photomicrographs are provided of filament cross sections in exemplary low shrink yarn portions (FIG. 4A) as well as in self textured high shrink yarn segments (FIG. 4B) after the resultant yarn 100′ has been subjected to a heat treatment. Because the magnification in FIGS. 4A and 4B is the same, and the cross section is from different sections of the post treatment resultant yarn, it can be seen that after post formation application of heat, the cross sections of the filaments in the low shrink segment are smaller than the cross sections of the filaments in the high shrink segment. In this regard it is contemplated that in order to realize the aesthetic and tactile benefits of the variable shrinkage zones along the resultant yarns 100′, the filaments making up the self-textured segments will preferably have an average diameter at least about 25 percent greater (more preferably at least about 50 percent greater) than the average diameter of the filaments forming the low shrink portions after being subjected to a post treatment heating. For yarns formed from either circular or non-circular filaments, the high shrink segments will preferably have an average cross-sectional area at least about 1.56 times (more preferably at least about 2.25 times) the average area of the filaments forming the low shrink segments. In the illustrated exemplary constructions, a comparison of the filaments of FIGS. 4A and 4B shows that some of the filaments in the self textured high shrink segments are at least twice the diameter of some of the filaments in the low shrink portions. Thus, for yarns formed from non-circular filaments it is contemplated that at least a portion of the filaments in the high shrink segments will have a cross-sectional area 4 times the area of some filaments forming the low shrink segments.

Crystalline Orientation

It has also been found that after heat treatment (such as occurs in fabric finishing) segments of the same resultant yarn 100′ treated according to the procedures as previously described are characterized by substantially different levels of crystalline orientation as measured by wide angle x-ray diffraction. In order to characterize the molecular structure of the two different types of domains in a finished construction, a polyester yarn treated according to the process as illustrated and described in relation to FIG. 1 was circularly knitted into a sock (i.e. a tube), dyed, and finished. The finished sock exhibited two distinct types of courses: open courses consisting of yarn that had low shrinkage during finishing, and tight courses consisting of yarn that had high shrinkage during finishing. FIG. 5 illustrates a zone in the sock containing these two regions. Importantly, it is to be understood that the same yarn is used throughout the sock and that the different zones emerged only after subsequent heat treatment.

To understand the differences in the zones of the sock individual courses of each type of region were removed from the construction for x-ray measurement. Courses were ‘double-folded’ to form a 4-ply yarn so as to increase the scattering signal rate and reduce the necessary exposure time. Samples were mounted onto standard x-ray sample mounts.

Wide-angle diffraction patterns were generated via exposure to x-rays generated with a rotating copper anode source having a primary wavelength of 1.5418 Å. Patterns were recorded using a general area detector system offset to an angle of 2

=16.5° and set 15 cm from the sample position. Samples were oriented in the beam such that the fiber axis was vertical. Exposures of 15 minutes were used to generate patterns, and a background pattern acquired over an empty position on the sample holder was subtracted from the resulting data.

The diffraction pattern for the high-shrink yarn sample is shown in FIG. 6A and that for the low-shrink yarn is shown in FIG. 6B wherein the lighter zones identify higher reflection intensity levels. Qualitatively, it was observed that in the two patterns the crystal plane reflections (the broad intensity peaks) in the high-shrink sample have a greater azimuthal spread than those in the low-shrink sample. It is known that the two primary causes of azimuthal spreading in multifilament fiber samples are misalignment of individual filaments and differences in the angular distribution of crystallites between the samples. Great care was taken during sample preparation to properly parallelize the filaments, and a slight tension was applied to maintain good orientation during handling and measurement. Thus, it is very unlikely that filament disorientation alone can account for the differences in angular peak distribution observed in the patterns. Therefore, it was determined that the azimuthal spread reflects a real difference in the angular distribution of crystallites between the two samples.

It is known that the difference in the angular distribution of crystallites between the two samples can be quantified in terms of the Herman orientation function: $f_{c} = \frac{{3\left\langle {{\cos\quad}^{2}\sigma} \right\rangle} - 1}{2}$ where σ is the relative angle of the PET chain axis. As will be appreciated, the Herman orientation function is a measure of the orientation of PET chains within fiber crystallites with respect to the fiber axis direction. It assumes values ranging from +1 (perfectly oriented parallel to the axis) to 0 (perfectly random) to −{fraction (1/2)} (perfectly oriented perpendicularly). For cylindrically symmetric (on average) fibers, the distributional average of the square cosine term is given by: $\left\langle {\cos^{2}\chi} \right\rangle = {\frac{\int_{0}^{\pi}{\cos^{2}\chi\quad{I_{P}(\chi)}\sin\quad\chi\quad{\mathbb{d}\chi}}}{\int_{0}^{\pi}{{I_{P}(\chi)}\sin\quad\chi\quad{\mathbb{d}\chi}}}.}$ Where /_(p)(λ) is the angular distribution of a directional vector P (in this case, the PET chain direction) as measured with respect to a reference direction, in this case the fiber axis.

In PET there does not exist a crystalline reflection in the direction of the PET chains. Thus, to determine the Herman orientation function for PET chains a well recognized geometric relationship is utilized to develop the square cosine term.

cos²σ

=1−0.8786

cos²λ₍₀₁₀₎

−0.7733

cos²λ₍₁₁₀₎

−0.348

cos²λ₍₁₀₀₎

, where σ is the relative angle of the PET chain axis, and λ_((hk0)) are the relatives angles of the (hk0) crystalline reflections. This relationship was described by Z. Wilchinsky in Journal of Applied Physics 30, 792 (1959) the contents of which are incorporated herein by reference.

The <cos²λ_((hk0))> terms can be numerically computed by extracting the /_((hk0))(λ) distributions from the measured diffraction patterns. Angular distributions were computed by integrating the pattern signals over a 0.7° range of 2{circle over (-)} values centered on the following positions: 17.65° for the (010) reflection, 22.75° for the (110) reflection, and 25.35° for the (100) reflection. Distributions of x-ray peaks for the high shrink and low shrink yarn segments (used for purposes of integration) are shown in FIGS. 7A and 7B. Because of the limited detector area, distributions were extrapolated out to the full 180° range by assuming the signal at high angles was due solely to amorphous scattering. This amorphous baseline was subtracted from the distributions before numerical integration.

Results from the numerical determination of the Herman orientation function (f_(c)) are shown in Table II below. As shown, the low-shrink yarn sample possessed a measurably higher level of orientation. TABLE II High Shrink Low Shrink <cos{circumflex over ( )}2(_(χ) 100)> 0.060 0.038 <cos{circumflex over ( )}2(_(χ) 110)> 0.087 0.062 <cos{circumflex over ( )}2(_(χ) 010)> 0.108 0.083 <cos{circumflex over ( )}2(σ)> 0.817 0.866 Herman fc 0.725 0.799

In order to confirm the legitimacy of the crystalline orientation evaluations on the treated yarn of the present invention, a control analysis was conducted on a standard fully drawn 265 denier 36 filament partially oriented PET yarn that had been cold drawn with a 2.1 draw ratio and heat set at 220° C. Three samples were taken from segments 6 to 12 inches apart along the length of the yarn and x-ray patterns were generated using 45 minute exposures. An air scattering frame was also acquired and subtracted from the data before analysis. The same calculations were performed as described above. The Herman orientation function calculated based on the measurements of these samples ranged from 0.819 to 0.853 which is a difference of 0.034. This is less than half the difference of 0.074 measured for the high shrink and low shrink portions of the yarn. Thus, there exists a much greater variation in crystalline orientation between portions of the yarns of the present invention following heat treatment than in standard yarns.

Based on the evaluations carried out it may be seen that the interlaced nodes along the yarn give rise to the high shrink portions of the yarn. Moreover, upon application of heat treatment these high shrink portions shrink to a greater degree and have a lower level of crystalline orientation (as measured by the Herman Orientation Function) than the low shrink portions. Moreover, the degree of variation in crystalline orientation along the length of the yarns of the present invention is substantially greater than variations in standard yarns.

Fabric Formation

In FIG. 8, there is illustrated a block diagram of a procedure for forming a fabric from the resultant yarn 100′. First, a POY yarn is purchased or made. Usually, this yarn has been spun to partially orient the fibers in the yarn, as shown in Step 181. Then, at Step 182 the POY yarn is underdrawn and simultaneously applied to a non-steady state rapid heat treatment to introduce variable heat history at different segments of the yarn as show and described above. At Step 183, a fabric is formed from resultant yarn having segments of differing heat treatment. At Step 184, the fabric is subjected to a heat treatment to cause selective shrinkage and self-texturing at discrete zones along the resultant yarn. The heat treatment in Step 184 can come from the heat setting of the fabric, the dyeing of the fabric, or other typical fabric processing. The resulting fabric has zones where the resultant yarn has shrunk and self textured, and zones where the resultant yarn did not shrink or self texture to the same extent. This often will give a fabric a surface textural, two-tone dyed appearance.

Flat Fabric

In FIG. 9 there is illustrated a typical prior art flat knit fabric 200 such as may be formed in a warp knit construction with elongated underlaps as will be well known to those of skill in the art. As shown, a face portion 201 of the fabric 200 is made up of a multiplicity of interconnected loops 202 formed from yarns 210. As illustrated, the face-forming yarns are made up of multiple discrete filaments 211. The yarns 210 in such prior art knit fabrics have typically undergone a hot drawing operation so as to impart a uniform heat treatment and extension to the filaments 211 prior to formation into the fabric 200. By way of example only, according to one typical process the yarns are fully drawn to approximately 1.7 times their initial length while being subjected to a temperature of about 200° C. prior to formation into a fabric construction. This drawing and heat treatment imparts enhanced crystallite orientation to the entire length of the yarn while also providing a substantially uniform heat history such that the propensity to undergo further shrinkage is minimized and any shrinkage which does occur after the yarn is formed into a fabric will be substantially uniform. Thus, the yarns forming the face portion 16 are of substantially uniform character upon initial formation and react in substantially the same manner when subjected to post-formation heat treatment such that uniform texture characteristics and filament alignment are maintained after the fabric is heat set and dyed.

As will be appreciated through reference to FIGS. 8 and 10, subsequent to the introduction of variable heat treatment across portions of the yarn to introduce the above-described variable shrinkage characteristics, the yarn resultant 100′ may thereafter be formed into a knit fabric similar in appearance to the knit fabric illustrated in FIG. 9. That is, the formed greige fabric is characterized by face-forming loops which are substantially uniform in texture. However, as illustrated in FIG. 10, due to the variable heat treatment history at segments along the face-forming yarns 100′, when the formed greige fabric is heat set and/or dyed at prolonged elevated temperatures, segments of the face-forming post treatment resultant yarn 100″ react in dramatically different fashions thereby imparting a variability to the finished fabric 300. In particular, portions of the post treatment resultant yarns 100″ which made up the interlace nodes 103 and adjacent areas and which did not undergo a uniform heat treatment during drawing tend to undergo selective shrinkage during the heat setting and/or dyeing operations, forming self textured loops 306 in the fabric 600. As explained above, this shrinkage occurs as a result of the fact that the shrinkage potential within these yarn zones has not been relieved previously. Conversely, the portions 306 of the post treatment resultant yarns 100″ which were in the loose portions 102 of the yarn between the interlace nodes 103, do not undergo substantial shrinking during the heat setting and/or dyeing operation since shrinkage potential has been relieved previously. The result is that the same yarn 100″ will have different loops 305 and 306 with different types of cross sections and crystalline orientation. As a result, a single post treatment resultant yarn can form one, two, three, or more self textured loops between one, two, three, or more standard loops on each side.

As will be appreciated, the heating may be carried out as a heat treatment during finishing, as an elevated dyeing treatment or any such other suitable elevated temperature operation as may be desired. As shown in FIG. 10, although the same yarns 100′ are utilized throughout the face portion 301 of the fabric 300, discrete segments of those yarns have undergone shrinkage so as to form self textured entangled segments 306 across the fabric. The segments of the yarns which have undergone uniform heat treatment during the initial warp drawing operation do not undergo such shrinkage and thus define arrangements of substantially unaltered surface loops 305 wherein the filaments remain substantially aligned with relatively low levels of crimping and entanglement.

As in the individual yarn samples evaluated, due to the differentiated shrinkage of the filaments at different yarn segments in the fabric, the filaments within the self textured segments 306 of the face are characterized by a substantially greater diameter than the filaments in the unaltered surface loops 305 and a different crystalline orientation, as previously described. By way of example only, for purposes of comparison refer to the photomicrographs of filament cross sections in exemplary low shrink yarn portions illustrated in FIG. 4A as well as in the self textured yarn segments illustrated in FIG. 4B. In this regard it is contemplated that in order to realize the aesthetic and tactile benefits of the variable shrinkage zones along the surface-forming yarns, the filaments making up the self-textured segments will preferably have an average diameter at least about 25 percent greater (more preferably at least about 50 percent greater) than the average diameter of the filaments forming the low shrink portions. For yarns formed from either circular or non-circular filaments, the high shrink segments will preferably have an average cross-sectional area at least about 1.56 times (more preferably at least about 2.25 times) the average area of the filaments forming the low shrink segments. In the illustrated exemplary constructions, a comparison of the filaments of FIGS. 4A and 4B shows that some of the filaments in the self textured high shrink segments are at least twice the diameter of some of the filaments in the low shrink portions. Thus, for yarns formed from non-circular filaments it is contemplated that at least a portion of the filaments in the high shrink segments will have a cross-sectional area 4 times the area of some filaments forming the low shrink segments.

By way of example only, within a resultant yarn 100′ according to the present invention it is contemplated that the number of interlace nodes will preferably be in the range of about 8 to 40 nodes per meter with each node taking up about 0.6 to about 1.3 cm. Thus, it is contemplated that zones of high retained shrinkage potential will preferably make up about 4.8% to about 52% percent of the total length of the yarn and will more preferably make up about 25% of the total length of the yarn.

As previously indicated, a substantial benefit of the present invention is that the self-textured segments of heat shrunk yarn are present across the surface of the fabric in a substantially random arrangement. This imparts a substantially natural random look which may be desirable in many instances. Moreover, since the self-textured zones undergo heat shrinkage as a result of activating intrinsic heat shrink potential, such shrinkage occurs without embrittlement thereby enhancing a soft feel and avoiding filament breakage leading to undesirable shredding. Also as previously indicated, after self-texturing takes place, the high shrink portions of the yarn have a lower level of crystalline orientation than the low shrink portions. In this regard it is contemplated that the level of crystalline orientation of the low shrink portions of the yarn as measured by the Herman Orientation Function will on average be at least 5% greater (and more preferably at least 10% greater) than the level of crystalline orientation of the high shrink portions.

The invention may be further understood through reference to the following non-limiting examples:

EXAMPLE I

A 115 denier 36 filament semi-dull round partially oriented polyester yarn was subjected to a 1.143 draw across a contact Dowtherm heater plate operated at a temperature of 200° C. The heater contact length was 17 inches and the yarn was taken up off of the heater at a rate of 600 yards per minute. The yarns were spaced at a density of approximately 17.4 yarns per inch across the heater. The warper tension was set at 25 to 30 grams. Overall draw ratio was 1.165. Measurements of the post drawn yarn indicated a linear density of 100.5 denier and a boiling water shrinkage of 10.0%. The drawn yarn was knitted into the face of a 2 bar Tricot knit fabric with the ground being formed of a 70 denier 36 filament semi-dull round fully warpdrawn polyester. The bar 1 (face yarn) runner length was 102 inches. The bar 2 (ground yarn) runner length was 46 inches. The knitting machine was fully threaded. The resultant fabric had 60 coarses per inch. The fabric was jet dyed according to a standard disperse dye cycle at 280° F., held for 20 minutes with a 2° F. per minute temperature ramp up. The fabric was wet pad tenter dried at a temperature of 300° F. passing through the tenter at 20 yards per minute. The exit width after drying was 59.5 inches. The resultant fabric had random high loops with relatively greater oriented crystalline regions than the low loops which were characterized by very low order orientation of the crystals as measured by wide angle X-ray scattering.

EXAMPLE 2

A 115 denier 36 filament semi-dull round partially oriented polyester yarn was subjected to a 1.143 draw across a contact Dowtherm heater plate operated at a temperature of 175 C. The heater contact length was 17 inches and the yarn was taken up off of the heater at a rate of 600 yards per minute. The yarns were spaced at a density of approximately 17.4 yarns per inch across the heater. The warper tension was set at 25 to 32 grams. Overall draw ratio was 1.165. Measurements of the post drawn yarn indicated a linear density of 100.0 denier and a boiling water shrinkage of 12.04%. The drawn yarn was knitted into the face of a 4 bar 56 gauge Raschel knit fabric. The bar 1 yarn (tie down stitch) bar 2 yarn (tie down stitch) and bar 4 (ground yarn) were all formed of 70 denier 36 filament semi-dull round fully warpdrawn polyester. The face yarn was threaded in Bar 3. The bar 1 runner length was 60 inches. The bar 2 runner length was 60 inches. The bar 3 (face yarn) runner length was 102 inches. The bar 4 ground yarn runner length was 54 inches. The resultant fabric had 49.5 coarses per inch. The fabric was jet dyed at 280° F., held for 20 minutes with a 20 F per minute temperature ramp up. The fabrics were wet pad tenter dried at a temperature of 300° F. passing through the tenter at 20 yards per minute. The exit width after drying was 53 inches. The resultant fabric had random high loops with relatively greater oriented crystalline regions than the low loops which were characterized by very low order orientation of the crystals as measured by wide angle X-ray scattering. The tiedown stitching pronounced the height of the tall loops.

Loop Pile Fabric

In FIG. 11 there is illustrated a typical prior art loop pile fabric 400 such as may be formed in a warp knit construction as will be well known to those of skill in the art. As shown, the loop pile fabric 400 has a base or a ground portion 410 formed from ground yarns 411. The pile fabric 400 also includes a pile portion 420 made up of a multiplicity of loops 424 formed from pile yarns 421 knitted in conjunction with the ground yarns 410. As illustrated, the pile yarns 421 are made up of multiple discrete filaments 422. The pile yarns 421 in such prior art pile fabrics have typically undergone a hot drawing operation so as to impart a uniform heat treatment and extension to the filaments 421 prior to formation into the fabric 400. By way of example only, according to one typical process the pile yarns 421 are fully drawn to approximately 1.7 times their initial length while being subjected to a temperature of about 200° C. prior to formation into a fabric construction. This drawing and heat treatment imparts enhanced crystallite orientation to the entire length of the yarn while also providing a substantially uniform heat history such that the propensity to undergo shrinkage is minimized and any shrinkage which does occur after the yarn is formed into a fabric will be substantially uniform. Thus, the pile yarns 421 yield loops 424 which are of substantially uniform character upon initial formation and which react in substantially the same manner when subjected to post-formation heat treatment such that uniform height characteristics and filament alignment are maintained after the fabric is heat set and dyed.

Illustrated in FIG. 12 is a pile fabric 500 has a base or ground portion 510 formed of ground yarns 511, and a pile portion 520 formed of pile yarns 521. As will be appreciated through reference to FIG. 8, the pile yarns 521 begin as the POY yarn 100 in Step 181, which are then formed into resultant yarns 100′ in Step 182 by the introduction of variable heat treatment across portions of the yarn 100 to introduce the above-described differential shrinkage potential characteristics in various segments in the resultant yarns 100′. In Step 183, the resultant yarn 100′ is formed into the pile fabric 500 as the pile yarns 521 of the pile portion 520 in a manner that the fabric is similar in appearance to the loop fabric illustrated in FIG. 11. That is, the formed greige fabric is characterized by loop heights which are substantially uniform. During the post fabric formation heat treatment of Step 184, the resultant yarn 100′ is transformed into the post heat treatment yarn 100″ giving the pile fabric 500 a substantially different appearance. Due to the variable heat treatment history at segments along the resultant yarns 100′, when the formed greige fabric is heat set and dyed at prolonged elevated temperatures, segments of the pile yarns 521 react in dramatically different fashions thereby imparting an appearance variability to the finished fabric 500. In particular, portions of the resultant yarns 100′ which made up the interlace nodes 103 and adjacent areas, and which did not undergo a uniform heat treatment during drawing, tend to undergo selective shrinkage during the heat setting and dyeing operations to form low profile loops 526. As explained above, this shrinkage occurs as a result of the fact that the shrinkage potential within these yarn zones has not been relieved previously. Conversely, the loose portions 102 of the pile forming yarns 100′ between the interlace nodes do not undergo substantial shrinking during the heat setting and dyeing operation since shrinkage potential has been relieved previously and form the high profile loops 525 with different cross sections and crystalline orientation than the low profile loops 526, as explained above.

FIG. 12 illustrates a resultant fabric structure following heat treatment and dyeing. As shown, although the same resultant yarns 100′ are utilized throughout the pile portion 520 of the fabric 500, portions of those yarns have undergone shrinkage so as to form low profile loop segments 526 of a self-textured entangled construction across the ground fabric 510. The segments of the yarns which have undergone uniform heat treatment during the initial drying operation do not undergo such shrinkage and thus define arrangements of high profile loops 525 wherein the filaments remain substantially aligned. The distribution of the low profile loops 526 and the high profile loops 525 is substantially random, and typically will group into zones on the fabric 500. In the fabric 500 illustrated in FIG. 12, a single post treatment resultant yarn 100″ can have at least one low profile loop 526 disposed between high profile loops 525, at least two low profile loops 526 disposed between high profile loops 525, and at least three low profile loops 526 are disposed between high profile loops 525. However, because of the randomness of the process, many more low profile loops 526 can be disposed between high profile loops 525, and the exact arrangement of the loops will be random. The randomness of the arrangement gives the pile fabric 500 a surface textural appearance. A photomicrograph illustrating such an exemplary fabric construction is provided at FIG. 13. In FIG. 13, the low profile loops 526 can be seen in the foreground and the high profile loops 525 can be seen directly behind the low profile loops 526.

As in the individual yarn samples evaluated, due to the differentiated shrinkage of the filaments at different yarn segments in the fabric, the filaments within the low profile loop segments 526 of the pile portion 520 are characterized by a substantially greater diameter than the filaments in the high profile loops 525. By way of example only, for purposes of comparison refer to the photomicrographs of filament cross sections in exemplary low shrink yarn portions illustrated in FIG. 4A as well as in the self textured yarn segments illustrated in FIG. 4B. In this regard it is contemplated that in order to realize the aesthetic and tactile benefits of the variable shrinkage zones along the pile-forming yarns the filaments making up the low profile loop segments will preferably have an average diameter at least about 25 percent greater (more preferably at least about 50 percent greater) than the average diameter of the filaments forming the high profile loops. Whether yarns with circular or non-circular filaments are used, the low profile loop segments will preferably have an average cross-sectional area at least about 1.56 times (more preferably at least about 2.25 times) the average area of the filaments forming the high profile loops. In the illustrated exemplary constructions, a comparison of the filaments of FIGS. 4A and 4B shows that some of the filaments in the low profile loop segments are at least twice the diameter of some of the filaments in the high profile loops. Thus, for yarns formed from non-circular filaments it is contemplated that at least a portion of the filaments in the low profile loop segments will have a cross-sectional area 4 times the area of some filaments forming the high profile loops.

By way of example only, within a yarn 100′ according to the present invention it is contemplated that the number of interlace nodes will preferably be in the range of about 8 to 40 nodes per meter with each node taking up about 0.6 to about 1.3 cm. Thus, it is contemplated that zones of high retained shrinkage potential will preferably make up about 4.8% to about 52% percent of the total length of the yarn and will more preferably make up about 25% of the total length of the yarn.

As previously indicated, a substantial benefit of the present invention is that the low profile loop segments 526 of heat shrunk yarn are present across the surface of the fabric in a substantially random arrangement. This imparts a substantially natural random look which may be desirable in many instances. Moreover, since the low profile zones undergo heat shrinkage as a result of activating intrinsic heat shrink potential, such shrinkage occurs without embrittlement and results in a self crimping of the yarns in the low profile zones which emulates texturing thereby enhancing a soft feel and avoiding filament breakage leading to undesirable shredding. As previously indicated, after self-texturing takes place, the high shrink portions of the yarn have a lower level of crystalline orientation than the low shrink portions. In this regard it is contemplated that the level of crystalline orientation of the low shrink portions of the yarn as measured by the Herman Orientation Function will on average be at least 5% greater (and more preferably at least 10% greater) than the level of crystalline orientation of the high shrink portions.

The invention may be further understood through reference to the following non-limiting example: EXAMPLE 3

A 115 denier 36 filament semi-dull round partially oriented polyester yarn was subjected to a 1.143 draw across a contact Dowtherm heater plate operated at a temperature of 170 C. The heater contact length was 17 inches and the yarn was taken up off of the heater at a rate of 600 yards per minute. The yarns were spaced at a density of approximately 17.4 yarns per inch across the heater. The warper tension was set at 26 to 30 grams. Overall draw ratio was 1.165. Measurements of the post drawn yarn indicated a linear density of 103.6 denier, a boiling water shrinkage of 11.16%, an elongation of 87.46% and a breaking strength of 267 grams. The drawn yarn was knitted into the face of a 2 bar 56 gauge POL knit fabric with the ground being formed of a single ply 150 denier 36 filament semi-dull round false twist textured polyester. The bar 1 (face yarn) runner length was 135 inches. The bar 2 (ground yarn) runner length was 52 inches. The knitting machine was fully threaded. The resultant fabric had 66 coarses per inch with a pile height of 0.065 inches and a width of 57.25 inches. Samples of the resultant greige fabric were thereafter subjected to heat setting at 330° F. and at 410° F. No difference in the finished fabrics was observed. The fabric heat treated at 410° F. The fabrics were jet dyed at 266° F., held for 30 minutes with a 2° F. per minute temperature ramp up. The fabrics were wet pad tenter dried at a temperature of 250° F. passing through the tenter at 25 yards per minute. The exit width after drying was 56 inches. The resultant fabric had random high loops with relatively greater oriented crystalline regions than the low loops which were characterized by very low order orientation of the crystals as measured by wide angle X-ray scattering.

Cut Pile Fabric

In FIG. 14 there is illustrated a typical prior art cut pile fabric 600, such as may be well known to those of skill in the art, having a base or a ground portion 610 formed from ground yarns 611 and pile portion 620 formed from a multiplicity of pile yarns 621. As illustrated, the pile yarns 621 are made up of multiple discrete filaments 622. The cut pile fabric can be formed by many methods know in the art, such as double needle bar, clip knit, tufting, POL knit, single needle bar, woven velour, etc. The pile yarns 621 in such prior art pile fabrics 600 have typically undergone a hot drawing operation so as to impart a uniform heat treatment and extension to the filaments 622 prior to formation into the fabric 600. By way of example only, according to one typical process the pile yarns 621 are fully drawn to approximately 1.7 times their initial length while being subjected to a temperature of about 200° C. prior to formation into a fabric construction. This drawing and heat treatment imparts enhanced crystallite orientation to the entire length of the yarn while also providing a substantially uniform heat history such that the propensity to undergo shrinkage is minimized and any shrinkage which does occur after the yarn is formed into a fabric will be substantially uniform. Thus, the pile yarns 621 yield pile yarns 621 which are of substantially uniform character upon initial formation and which react in substantially the same manner when subjected to post-formation heat treatment such that uniform height characteristics and filament alignment are maintained after the fabric is heat set and dyed.

Illustrated in FIG. 17 is a cut pile fabric 700 that has a base or ground portion 710 formed of ground yarns 711, and a pile portion 720 formed of pile yarns 721. As will be appreciated through reference to FIG. 8, the pile yarns 721 begin as the POY yarn 100 in Step 181 which is formed into a resultant yarns 100′ after the introduction of variable heat treatment across portions of the yarn 100 in Step 182 to introduce the above-described differential shrinkage potential characteristics in various segments in the resultant yarns 100′. In Step 183, the resultant yarn 100′ is formed into the pile fabric 700 as the pile yarns 721 of the pile portion 720 in a manner that the fabric is similar in appearance to the cut pile fabric illustrated in FIG. 13. That is, the formed greige fabric is characterized by pile heights which are substantially uniform. During the post fabric formation heat treatment of Step 184, the resultant yarn 100′ is transformed into the post heat treatment yarn 100″, giving the pile fabric 700 a substantially different appearance. Due to the variable heat treatment history at segments along the resultant yarns 100′, when the formed greige fabric is heat set and dyed at prolonged elevated temperatures, segments of the pile yarns 721 react in dramatically different fashions thereby imparting an appearance variability to the finished fabric 700. In particular, portions of the resultant yarns 100′ which made up the interlace nodes 103 and adjacent areas and which did not undergo a uniform heat treatment during drawing tend to undergo selective shrinkage during the heat setting and dyeing operations to form low profile cut pile 726. As explained above, this shrinkage occurs as a result of the fact that the shrinkage potential within these yarn zones has not been relieved previously. Conversely, the loose portions 102 of the pile forming yarns 100′ between the interlace nodes do not undergo substantial shrinking during the heat setting and dyeing operation since shrinkage potential has been relieved previously, and those portions form the high profile cut pile 725 with different cross sections and crystalline orientation than the low profile loops 726, as explained above.

FIG. 15 illustrates a resultant fabric structure following heat treatment and dyeing. As shown, although the same resultant yarns 100′ are utilized throughout the pile portion 720 of the fabric 700, portions of those yarns have undergone shrinkage so as to form low profile loop segments 726 of a self-textured entangled construction across the ground fabric 710. The segments of the resultant yarns 100′ which have undergone uniform heat treatment during the initial drying operation do not undergo such shrinkage and thus define arrangements of high profile pile yarns 725 wherein the filaments remain substantially aligned. The distribution of the low profile pile yarns 726 and the high profile pile yarns 725 is substantially random, and typically will group into zones on the fabric 700. In the fabric 700 illustrated in FIG. 12, a single post treatment resultant yarn 100″ can form a row of pile yarns 7210 having at least one low profile pile yarn 726 disposed between high profile pile yarns 725, at least two low profile pile yarns 726 disposed between high profile pile yarns 725, and at least three low profile pile yarns 726 disposed between high profile pile yarns 725. However, because of the randomness of the process, many more low profile pile yarns 726 can be disposed between high profile pile yarns 725, and the exact arrangement of the various height pile yarns will be random. The randomness of the arrangement gives the pile fabric 700 a surface textural appearance. A photomicrograph illustrating such an exemplary fabric construction is provided at FIG. 16. In FIG. 16, the low profile pile 726 can be seen in the foreground and the high profile pile 725 can be seen directly behind the low profile pile 726.

As in the individual yarn samples evaluated, due to the differentiated shrinkage of the filaments at different yarn segments in the fabric, the filaments within the low profile pile yarn segments 726 of the pile portion 720 are characterized by a substantially greater diameter than the filaments in the high profile pile yarns 725. By way of example only, for purposes of comparison refer to the photomicrographs of filament cross sections in exemplary low shrink yarn portions illustrated in FIG. 4A as well as in the self textured yarn segments illustrated in FIG. 4B. In this regard it is contemplated that in order to realize the aesthetic and tactile benefits of the variable shrinkage zones along the pile-forming yarns the filaments making up the low profile loop segments will preferably have an average diameter at least about 25 percent greater (more preferably at least about 50 percent greater) than the average diameter of the filaments forming the high profile loops. Whether yarns with circular or non-circular filaments are used, the low profile loop segments will preferably have an average cross-sectional area at least about 1.56 times (more preferably at least about 2.25 times) the average area of the filaments forming the high profile loops. In the illustrated exemplary constructions, a comparison of the filaments of FIGS. 4A and 4B shows that some of the filaments in the low profile pile yarn segments are at least twice the diameter of some of the filaments in the high profile pile yarns. Thus, for yarns formed from non-circular filaments it is contemplated that at least a portion of the filaments in the low profile pile yarn segments will have a cross-sectional area 4 times the area of some filaments forming the high profile pile yarns.

By way of example only, within a yarn 100′ according to the present invention it is contemplated that the number of interlace nodes will preferably be in the range of about 8 to 40 nodes per meter with each node taking up about 0.6 to about 1.3 cm. Thus, it is contemplated that zones of high retained shrinkage potential will preferably make up about 4.8% to about 52% percent of the total length of the yarn and will more preferably make up about 25% of the total length of the yarn.

As previously indicated, a substantial benefit of the present invention is that the low profile pile yarn segments 726 of heat shrunk yarn are present across the surface of the fabric in a substantially random arrangement. This imparts a substantially natural random look which may be desirable in many instances. Moreover, since the low profile zones undergo heat shrinkage as a result of activating intrinsic heat shrink potential, such shrinkage occurs without embrittlement and results in a self crimping of the yarns in the low profile zones which emulates texturing thereby enhancing a soft feel and avoiding filament breakage leading to undesirable shredding. As previously indicated, after self-texturing takes place, the high shrink portions of the yarn have a lower level of crystalline orientation than the low shrink portions. In this regard it is contemplated that the level of crystalline orientation of the low shrink portions of the yarn as measured by the Herman Orientation Function will on average be at least 5% greater (and more preferably at least 10% greater) than the level of crystalline orientation of the high shrink portions.

The invention may be further understood through reference to the following non-limiting example:

EXAMPLE 4

A 175 denier 48 filament full dull round partially oriented polyester yarn was subjected to a 1.143 draw across a contact Dowtherm heater plate operated at a temperature of 215° C. The heater contact length was 17 inches and the yarn was taken up off of the heater at a rate of 600 yards per minute. The yarns were spaced 17.4 yarns per inch across the heater. The warper tension was 48 grams. Overall draw ratio was 1.165. Measurements of the post drawn yarn indicated a linear density of 151.8 denier and a boiling water shrinkage of 12.66%. The drawn yarn was knitted in the face of a 6-bar 32 gauge Double Needle Bar Knit machine with the ground being formed of a 150 denier 36 filament semi-dull round warp drawn polyester and a 212 denier 36 filament semi-dull round underdrawn polyester. The bar {fraction (3/4)} (pile yarns) runner length was 375 inches. The bar 2/5 (ground yarns) runner length was 90 inches and the bar 1/6 (ground yarn) runner length was 130 inches. The knit machine was fully threaded. The resultant sandwich fabric had a thickness of 0.205 inches and was subsequently slit to yield a pile height of {fraction (6/64)} inches. Samples of the resultant greige fabric were thereafter subjected to heat setting at 330° F. and at 410° F. No difference in the finished fabric was observed. The fabrics were jet dyed at 266° F., held for 30 minutes with a 2° F. per minute rate of rise. The fabrics were wet pad tenter dried at a temperature of 250° F. passing through the tenter at 25 yarns per minute. The exit width was 56 inches. The resultant fabric was characterized with a “pebbly” surface appearance. 

1. A cut yarn pile fabric comprising a base portion and a pile portion, wherein the pile portion comprises a first group of cut yarn piles projecting outwardly from the base portion to a first height and at least a second group of cut yarn piles projecting outwardly from the base portion to a second height lower than the first height, wherein at least a portion of the first group of cut yarn piles and at least a portion of the second group of cut yarn piles are formed from segments of a common yarn and wherein in the fabric the segments of the common yarn forming the second group of cut yarn piles comprise a plurality of yarn filaments characterized by an average cross-sectional area at least 1.56 times the average cross-sectional area of yarn filaments in the segments of the common yarn forming the first group of cut yarn piles.
 2. The invention as recited in claim 1, wherein the cut yarn pile fabric is a knit fabric.
 3. The invention as recited in claim 2, wherein the loop pile fabric is a double needlebar knit fabric.
 4. The invention as recited in claim 2, wherein the loop pile fabric is a clip knit fabric.
 5. The invention as recited in claim 2, wherein the loop pile fabric is a POL knit fabric.
 6. The invention as recited in claim 1, wherein the common yarn is a multi-filament thermoplastic yarn.
 7. The invention as recited in claim 6, wherein the material of the common yarn is selected from the group consisting of polyester, polypropylene, and nylon.
 8. The invention as recited in claim 1, wherein the segments of the common yarn forming the second group of cut yarn piles comprise a plurality of yarn filaments having a lower degree of crystalline orientation than the yarn filaments in the segments of the common yarn forming the first group of cut yarn piles such that the average level of crystalline orientation of yarn filaments in the segments of the common yarn forming the first group of cut yarn piles as measured by the Herman Orientation Function is at least 5% greater than the average level of crystalline orientation of the yarn filaments in the segments of the common yarn forming the second group of cut yarn piles.
 9. The invention as recited in claim 1, wherein the segments of the common yarn forming the second group of cut yarn piles are characterized by a substantially non-parallel arrangement of crimped yarn filaments.
 10. The invention as recited in claim 1, wherein the segments of the common yarn forming the second group of cut yarn piles comprise a plurality of substantially circular cross-section yarn filaments characterized by an average cross sectional diameter which is at least 50 percent greater than the average cross sectional diameter of yarn filaments in the segments of the common yarn forming the first group of cut yarn piles.
 11. The invention as recited in claim 10, wherein at least a portion of the yarn filaments in the segments of the common yarn forming the second group of cut yarn piles are characterized by a cross sectional diameter which is at least twice the cross sectional diameter of one or more yarn filaments in the segments of the common yarn forming the first group of cut yarn piles.
 12. A cut yarn pile fabric comprising a base portion and a pile portion, wherein the pile portion comprises a first group of cut yarn piles projecting outwardly from the base portion to a first height and at least a second group of cut yarn piles projecting outwardly from the base portion to a second height lower than the first height, wherein at least a portion of the first group of cut yarn piles and at least a portion of the second group of cut yarn piles are formed from segments of a common yarn and wherein in the fabric the segments of the common yarn forming the second group of cut yarn piles comprise a plurality of yarn filaments characterized by an average cross-sectional area which is at least 1.56 times the average cross sectional diameter of yarn filaments in the segments of the common yarn forming the first group of cut yarn piles and wherein the yarn filaments in the segments of the common yarn forming the second group of cut yarn piles are characterized by a lower degree of crystalline orientation than the yarn filaments in the segments of the common yarn forming the first group of cut yarn piles such that the average level of crystalline orientation of yarn filaments in the segments of the common yarn forming the first group of cut yarn piles as measured by the Herman Orientation Function is at least 5% greater than the average level of crystalline orientation of the yarn filaments in the segments of the common yarn forming the second group of cut yarn piles.
 13. The invention as recited in claim 12, wherein the common yarn is a multi-filament polyester yarn.
 14. The invention as recited in claim 13, wherein the average level of crystalline orientation of yarn filaments in the segments of the common yarn forming the first group of cut yarn piles as measured by the Herman Orientation Function is at least 10% greater than the average level of crystalline orientation of the yarn filaments in the segments of the common yarn forming the second group of cut yarn piles.
 15. The invention as recited in claim 12, wherein the segments of the common yarn forming the second group of cut yarn piles are characterized by a substantially non-parallel arrangement of crimped yarn filaments.
 16. The invention as recited in claim 15, wherein at least a portion of the yarn filaments in the segments of the common yarn forming the second group of cut yarn piles are substantially circular cross-sectional filaments characterized by a cross sectional diameter which is at least twice the cross sectional diameter of one or more yarn filaments in the segments of the common yarn forming the first group of cut yarn piles.
 17. A method of forming a cut yarn pile fabric comprising a base portion and a pile portion, wherein the pile portion comprises a first group of cut yarn piles projecting outwardly from the base portion to a first height and at least a second group of cut yarn piles projecting outwardly from the base portion to a second height lower than the first height, the method comprising the steps of: underdrawing a partially oriented multi-filament yarn across a heat source at a rate such that portions of the yarn undergo substantially complete heat setting and other portions do not undergo substantially complete heat setting; forming the yarn into the cut pile portion of the cut yarn pile fabric; and heating the fabric such that portions of the yarn which did not undergo substantially complete heat setting during the underdrawing step shrink towards the base portion of the fabric in a crimped self texturing manner. 